1. Field of the Invention
The present invention relates to a window for automobiles or the like, including a window plate and a frame member composed of a thermoplastic synthetic resin material and provided integrally with the window plate, and also to a method of manufacturing such windows.
2. Description of the Related Art
Automobile windows wherein a window plate is integrally provided with a frame member composed of a thermoplastic synthetic resin material is advantageous in that, since it is not necessary to prepare a window molding member as a separate component from the window plate, the number of components and assembly steps can be reduced to realize an improved manufacturing productivity in the assembly lines of automobile factories.
There is disclosed, e.g. in U.S. Pat. No. 4,139,234 and Japanese Patent Application Laid-open Publication Nos. 56-99,817 and 57-1,737, a method of manufacturing such automobile windows wherein the peripheral edge of a window plate is placed in an injection mold including upper and lower mold halves, and a molten thermoplastic synthetic resin material is injected into the cavity space between the upper and lower mold halves through at least one gate. While the above-mentioned method permits formation of an integral frame member along the edge of the window plate, a number of problems are left still unsolved, which are as follows.
First of all, thermoplastic synthetic resin material may have a relatively high viscosity during the injection into the mold cavity, which depends upon physical and/or chemical properties of the material. Then, the injection has to be carried out at an elevated temperature of the mold to lower the viscosity of the resin material and to avoid premature cooling of the resin material before it has been completely distributed within the mold cavity. The injection also has to be carried out under a relatively high injection pressure to realize a uniform distribution of the resin material throughout the entire cavity space. The elevated temperature to which the mold has to be heated necessarily requires a longer time until completion of the injection and cooling of the resin material, and makes it difficult to achieve an improved manufacturing productivity. Furthermore, the relatively high injection pressure often results in undesirable formation of burrs or flushings along the parting surface of the mold halves, or results in damage to of the window plate due to a higher tightening force applied from both sides by the mold halves for withstanding the injection pressure. Also, when the frame member is to be provided with an integral, strip-like ornamental element applied on its outer surface with clips or with the like fitting elements partly embedded in the synthetic resin material by a so-called insert-molding process, these elements may be deformed or subjected to dislocation by the injection pressure.
Secondly, the frame member placed to cool is more or less accompanied by shrinkage, thereby subjecting the window plate to a severe compression stress. Thus, when the window plate is composed of a brittle glass plate, it is not always possible to prevent formation of cracks in the window plate. Particularly when the window plate has a surface curvature, the window plate is often subjected to a substantial bending stress; and the curved surface of the window plate undergoes an undesirable deformation. These problems are more significant when the window plate is composed of a transparent synthetic resin material with a relatively lower structural rigidity than inorganic glass. Moreover, the frame member is generally formed to surround the edge of the window plate from both sides thereof, and thus includes a substantially U-shaped cross-sectional portion formed of relatively thin lip and web sections on the outer and rear surfaces of the window plate, respectively, and a relatively thick bridge section for connecting the lip and web sections with each other. The material thickness of the frame member with such a sudden change results in a retarded cooling rate of the thick bridge section and results in a resultant formation of a sink mark on its outer surface.
Finally, in addition to the above, the window plate is accompanied by certain dimensional fluctuations which are due to practical difficulties in preparing window plates of a satisfactorily constant shape, while the volume of the mold cavity remains always constant. An optimum amount of thermoplastic synthetic resin material to be injected into the mold cavity thus varies for each window plate, depending upon the length with which the window plate is inserted into the mold cavity. From practical viewpoint, however, it is not very appropriate to individually adjust the amount of the resin material for each shot, and it has thus been a general practice to inject into the mold cavity a substantially constant amount of resin material, without regard to dimensional fluctuation of the window plate at all. It is of course that injection of an excessive amount of resin material into the mold cavity, which also, results in formation of burrs or flushings along the parting surface of the mold halves, while insufficiency in the injected amount of the resin material gives rise to an undesirable tendency of the sink mark to appear on the outer surface of the frame member.